1. Field of the Invention
The invention relates to an ink jet recording head having a plurality of nozzle openings disposed in a sheet forwarding direction, with each nozzle opening jetting an ink droplet due to pressure provided by a pressure producing chamber. More particularly, the invention is directed to a nozzle opening arrangement on the ink jet recording head.
2. Description of the Related Art
Ink jet recording heads are widely used throughout the printing industry. Such ink jet recording heads exhibit high recording density, are capable of printing dots of various sizes, and are relatively quiet during operation.
Two basic types of ink jet recording heads exist. A bubble jet type recording head uses thermal energy provided by a heater to effect printing. On the other hand, in a piezoelectric vibration element driven recording head, the displacement of piezoelectric vibration elements causes ink to be omitted to effect printing.
Two general types of piezoelectric vibration element driven recording heads exist. In the first type, vertical vibration of the piezoelectric vibration elements causes ink to be emitted. In the second type, flexural vibration of the piezoelectric vibration elements causes ink to be emitted.
In the first type of piezoelectric vibration element driven recording heads, the area in which a piezoelectric vibration element abuts against the vibration plate can be reduced. Hence, the interval between the nozzle opening arrays can easily be made small. However, the process for assembling such a recording head is complicated because each piezoelectric vibration element is extremely small.
The second type of piezoelectric vibration element driven recording heads employs a laminated structure, such as described in Japanese Unexamined Patent Publication No. 4-366643. That is, a common ink supply section, and pressure producing chambers or ink flow paths, are first formed in each of a plurality of thin plate members. These thin plate members are then sequentially laminated on the back of a nozzle plate. Accordingly, the assembly process is simple.
However, in this arrangement, each flow path extending from the pressure producing chamber to the nozzle openings is formed by making communicating holes in each thin plate member, and arranging these communicating holes proximate to one another. Hence, it is difficult to discharge the tiny air bubbles in the ink from the corners of the flow paths formed in each thin plate member.
In addition, in this arrangement, the size of the piezoelectric vibration plate mounted on the pressure producing chamber is larger than that of the piezoelectric vibration plate used as the piezoelectric vibration element in the first type of piezoelectric vibration element driven recording head. Hence, the distance between the nozzle opening arrays is increased.
If the distance between the nozzle opening arrays is increased, error between dots printed on a recording sheet in the auxiliary scanning direction tends to increase if three or more nozzle opening arrays are formed in an attempt to improve printing quality. In this case, however, printing quality is actually reduced.
That is, a recording head having a plurality of nozzle opening arrays is designed so that each nozzle opening array enables a dot to be printed at a predetermined position in the auxiliary scanning direction. As a result, this type of recording head has the uppermost nozzle opening and the lowermost nozzle opening arranged at opposite ends in the main scanning direction. This causes an error of G.times.sin.theta. between lines in the auxiliary scanning direction before and after sheet forwarding, assuming that the distance between the nozzle opening array at one end and the nozzle opening array at the other end in the main scanning direction is G, and the angle of inclination between the direction in which the nozzle opening arrays of the recording head extend and the sheet forwarding direction is .theta.. This error, G.times.sin.theta., causes white lines and black lines to be intermingled during printing, thereby impairing painting quality.
An ink jet recording head designed to eliminate this problem is described in European Laid-open Patent Publication No. 554907. In this ink jet recording head, four nozzle opening arrays, each having a plurality of nozzle openings linearly pitched in the sheet forwarding direction at an interval corresponding to the number of nozzle opening arrays, have their positions in the main scanning direction staggered by a predetermined interval so as to be different from the physically arranged sequence thereof. This arrangement, which reduces the distance in the auxiliary scanning direction between the uppermost nozzle opening and the lowermost nozzle opening of the recording head, can prevent printing of white lines and black lines due to displacement in the angle .theta. between the nozzle opening array and the sheet forwarding direction.
However, this advantage is realized only when the number of nozzle opening arrays is four. Hence, such a design is applicable to a limited number of recording heads.